1. Field of the Invention
The invention relates in general to an illumination device, and more particularly, to an illumination device used in a display.
2. Description of the Related Art
The conventional projection apparatus has been widely applied in front projection type or large panel rear projection type displays. The required source has to provide enough luminance. Typically, light sources such as halogen lamps, arc lamps, for example, high pressure mercury lamps, metal halogen lamps, xenon lamps are employed. These lamps have the advantage of high luminance, but on the other side, have the disadvantages of high electricity consuming, short lifetime, and high temperature. These light sources are thus selected only while a high luminance is required.
FIG. 1A and FIG. 1B show two types of conventional illumination devices. FIG. 1A is a schematic drawing of a projection apparatus disclosed in U.S. Pat. No. 5,418,583. A first lens array 20 and a second lens array integrator 30 are used to uniformize a light source 10, and to project the light source 10 onto a liquid crystal display (LCD) light valve 40. FIG. 1B is a schematic drawing of a projection apparatus disclosed in U.S. Pat. Nos. 4,656,562 and 5,634,704. A glass rod integrator 25 and a lens 35 are used to uniformize a light source 10, and to project the light source 10 onto a liquid crystal display (LCD) light valve 40. In both of the projection apparatus shown in FIG. 1A and FIG. 1B, a halogen lamp or various type of arc lamp is used as the light source 10. Therefore, the projection apparatus has very high electricity consumption, a short life time, and high temperature and is not suitable for use in a small scale display.
The diagonal length of a desktop display screen is typically in a range of about 20 inch to 30 inch. The required luminance of the light source is not as high as the front projection type or large panel back projection type displays. Moreover, the desktop screen is often in a ON status, so the light source has to keep supplying a light. Therefore, the conventional light source with a high electricity consumption, short lifetime, and a high operation temperature is not suitable to apply in a desktop display screen.